AUTOSPORT's Formula 1 2015 grid guide

The wait is over. Formula 1 returns this weekend with the now-traditional curtain-raiser that is the Australian Grand Prix, with everybody bar Mercedes unsure of where they will sit in the pecking order.

For some, like Mercedes and Williams, consistency reigns for 2015. For others, like Ferrari, the revived McLaren-Honda allegiance and Renault's main contender Red Bull, the off-season has ranged from wholesale change to shaking up its driver line-up.

We've already had a phoenix from the ashes thanks to the Manor-Marussia revival, and political wrangling as the usually-neutral Sauber fights against former employee Giedo van der Garde in the Australian courtroom.

It's an indicator of the storylines set to intrigue across the next eight months on motorsport's biggest stage. Here, AUTOSPORT guides you through the main players.

Reigning champion Mercedes heads into 2015 as clear favourite for more success after a hugely encouraging winter-testing programme.

Quickest overall on single lap pace - even though it never used the fastest super-soft tyre - Mercedes' long-run form suggests a decent edge over the opposition too.

The W06 certainly appears to have delivered the step forward in downforce and power that the team had hoped to gain over its predecessor.

Although both Nico Rosberg and Lewis Hamilton have talked about difficulties in finding the perfect balance for their car over the winter, equally neither particularly struggled to produce impressive lap times.

Few will be surprised if during the early stages of the campaign it is a straight fight between last year's title contenders for race victories again.

Perhaps the only question mark that surrounds Mercedes is whether it has got on top of the reliability issues that overshadowed its 2014 campaign.

While there have been days in testing when it has completed more than 150 laps, there were times when little niggles caused stoppages, too.

One other thing to keep an eye out for is how the relationship between Hamilton and Rosberg develops, and if tensions will again cause a few headaches for the bosses.

Lewis Hamilton is such an exciting driver to watch not just because of his amazing natural talent, but for the fact he can be so unpredictable.

When he is at the peak of his game, he is simply unbeatable: as team-mate Nico Rosberg found out to his cost when Hamilton won six of the final seven races last year.

But equally, as a driver who wears his heart on his sleeve, there can be afternoons where errors slip in and Hamilton throws away golden opportunities.

It's that uncertainty about what Hamilton will produce on the day that still leaves the title battle well open - and gives Rosberg big hope that he can go one better and beat his British rival this time out.

Rosberg delivered his best season in F1 last year, but it was not quite good enough to take him all the way to championship glory.

The margins were slim, however. Slightly better reliability and ironing out one or two errors would have been enough to make a big difference in the end.

Rosberg is a hard worker - every lesson from the 2014 campaign will have been taken on board, analysed and learned from to ensure that he does not let any opportunity go begging this year.

He was fully on top of qualifying last season, but knows that he must improve his overall race form to take the fight to Hamilton. It's something he is confident he can do.

You could be forgiven for thinking it feels like the end of an era at Red Bull, with design genius Adrian Newey taking a backseat in the drawing room and four-time world champion Sebastian Vettel departed for Ferrari.

But that doesn't mean the Milton Keynes outfit isn't still a force to be reckoned with in Formula 1.

Newey always went to great lengths to praise the team around him for helping to produce Red Bull's succession of title-winning cars and, though not as successful as its predecessors, last year's RB10 was still reckoned by many to be the best chassis in the field.

According to team insiders, RB11 is even better, so it seems much will depend on what engine partner Renault - confident in its development curve but admittedly behind schedule - can come up with this year.

Early signs are that reliability is better, while extra power is there but not yet easily translated onto the track.

Team boss Christian Horner reckoned 2014 was arguably Red Bull's best in terms of maximising strategy and grabbing the opportunities that came its way, so there's an argument to say the four-time world champion squad is as operationally sharp as ever heading into the new season.

Retaining emerging superstar Daniel Ricciardo on the driving strength is a massive plus for Red Bull's competitive prospects. After all, this is a man whose speed and guile helped drive Vettel out in the first place...

The Australian is Red Bull's new 'smiling assassin' (a nickname bestowed previously on Vettel) - happy-go-lucky outside the car, a ruthless racer inside it.

With Vettel now re-housed at Maranello, Ricciardo will become the focal point for Red Bull's competitive energies. The team clearly believes in him, and Ricciardo's confidence is sky-high following a breakout season in which he won three races, and seriously impressed Fernando Alonso...

Team-mate Daniil Kvyat has the difficult task of following Ricciardo's example. His challenge is arguably greater given he has the benefit of just 19 grand prix starts to fall back on.

Red Bull admits it has promoted the 20-year-old Russian from Toro Rosso earlier than it would have liked, but that doesn't mean it's simultaneously going to cut him extra slack.

The pressure will be on to deliver straightaway inside a top team. In fairness, Red Bull insiders have every faith Kvyat is made of the right stuff to rise to that challenge.

Williams ended last season as the closest challenger on merit to world champion Mercedes. It was quite some feat considering the Grove-based outfit limped to ninth place in the constructors' championship the previous season - its worst performance in more than a decade.

But the arrival of Pat Symonds as technical director has proved inspired while Rob Smedley has begun improving the team operationally in his role as head of vehicle performance. Williams looks like the team of old once more - and it is doing it as a customer team against the might of the manufacturers.

Winter testing was super smooth and the car looks like a step forward. Both Felipe Massa and Valtteri Bottas have said the car feels better, with improvements in stability, but it was clear they were a little taken aback by Mercedes' impressive form in testing.

Hanging onto Mercedes' coattails will be tough this season, while chief test and support engineer Rod Nelson admits the team faces a scrap with Ferrari.

At least early in the season, the team is expecting to be challenging for podiums and in the ballpark for a win but from then on it will face a battle from the 'works' outfits of Ferrari and the Red Bull-Renault package as they accelerate development.

There's very much a fire-and-ice element to the Williams driver line-up.

The calm and collected Valtteri Bottas was the team's leading light last year, but Felipe Massa showed that despite a turbulent end to his time with Ferrari there's still plenty of heat in the Brazilian's belly.

Both are confident that Williams has made a step forward over the winter and each has his own motivation for wanting to land a first win for a Martini-liveried Formula 1 car since the 1970s.

Last season was a breakthrough year for Bottas, who could well have ended up third in the drivers' standings but for a slightly slow start. The Finn showed just why he is so highly rated with a string of impressive performances, suggesting it is only a matter of when he will claim a maiden victory.

Massa, by contrast, had a season littered with highs and lows and was only seventh in the points, three places below his younger, less-experienced team-mate.

But it was the Brazilian who took the team's only pole of the season and it was the Brazilian who almost landed victory for Williams in the Abu Dhabi Grand Prix.

It shows that Williams is very well-placed on the driver front heading into 2015.

A new era has begun at Ferrari - with sweeping changes in management and on the driver front that it hopes will turn around the team's recent downturn in form.

Gone are Luca di Montezemolo, Marco Mattiacci and Fernando Alonso plus a host of technical staff. In have come Sergio Marchionne, Maurizio Arrivabene and Sebastian Vettel to instil change that they hope will put Ferrari back at the centre of Formula 1.

With highly rated technical director James Allison having been left alone to focus on producing the best car possible - with assistance from a revamped engine department - the early signs are of a decent step forward on track.

Off it too there is a renewed enthusiasm and aggression to start doing things differently. Just look at the provocation caused by Ferrari's concept F1 car and Arrivabene's grandstand protest in Barcelona testing.

It's results that the team really needs though, and the new SF15-T certainly appears much better than its predecessor. Kimi Raikkonen in particular is benefiting from a strong front end that should allow him to recapture some of his old magic.

Do not imagine for a second, though, that Ferrari is ready to overhaul Mercedes just yet. Getting closer will be enough this season, but there is a long road to recovery.

The team has openly talked about aiming for two wins - but even that will be a tough call judging by how impressive Mercedes has been in the build-up to the new season.

Sebastian Vettel was in need of fresh motivation after the glory times came to an end at Red Bull. At Ferrari, he appears to have found just that, having arrived at the perfect time to make the most of recent gains.

New management is sweeping change through Maranello, and Vettel is relishing life as a Ferrari driver.

The new SF15-T is a clear step forward over its predecessor, and Vettel's hard work ethic, twinned with his fun personality, has been embraced by his Italian colleagues.

It may be too much to consider title talk yet, but wins must be on the cards on days when the mighty Mercedes makes errors.

Kimi Raikkonen heads into 2015 like a man reborn, as the nightmares of his 2014 campaign have been swiftly erased.

His return to Ferrari last year was nothing short of a huge disappointment as he struggled massively with a lack of feel from the front end of the car. Attempts by Ferrari to cure the problems did not succeed and it led to a season of frustration.

The 2015 Ferrari has been built around Raikkonen's needs, which is why he has felt more at home from the first time he stepped into the car.

Progress with aerodynamics and engines should further help Raikkonen rediscover some of his old form - and enjoy what will be a fierce battle with new team-mate Vettel.

Fans of McLaren are having their patience sorely tested at the moment. The Woking team is currently on its longest losing streak (38 races and counting) since it failed to top the podium for three straight seasons in the mid-1990s.

There is much strong rhetoric about its revived engine partnership with returning manufacturer Honda. Talk of "ambitious" ERS systems and "aggressive" 'size-zero' aerodynamics has surrounded the new MP4-30.

But pre-season went badly for McLaren-Honda. The car has so far proved unreliable and off the pace.

So the talk now is of "potential", which the team admits it won't even begin to realise until the early-season flyaway races are out of the way.

The good news is that racing director Eric Boullier has finished restructuring the team (and is happy with the results), while the MP4-30 is already faster than its predecessor - even propelled by a troublesome Honda engine not running at full power.

McLaren is also convinced the influence of ex-Red Bull aerodynamicist Peter Prodromou will help return it to winning ways - eventually.

For now, though, fans of this great British squad will need to exercise a little more of that patience while McLaren-Honda finds its feet.

After the 'spygate' saga that led to McLaren's exclusion from second place in the 2007 world championship, many doubted a reunion between 'enfant terrible' Fernando Alonso and the team built by Ron Dennis could ever happen.

But it has. Dennis says he has "mellowed" since that infamous season, while Alonso says he is more "mature".

Since leaving Ferrari, Alonso has maintained he is fully committed to McLaren-Honda, and prepared to wait for the package to come good.

But the paddock knows this was not Alonso's first choice. He wanted Lewis Hamilton's Mercedes seat, then he wanted Sebastian Vettel's Red Bull seat.

He got neither, so this is a (re)marriage of convenience.

McLaren-Honda has gone to great lengths (and considerable expense) to recruit a driver who for many is the most complete racer on the grid today, while the double world champion is fast running out of time to win the third world title he so desperately craves.

This marriage really needs to work second time around.

McLaren agonised over whether 2009 world champion Jenson Button, or his 2014 rookie team-mate Kevin Magnussen, should partner Alonso.

It (eventually) opted for Button - a classy operator, who knows Honda well, and can be counted on to bring home big points if the car is working well. But Magnussen is back in for Melbourne while Alonso recovers fully from the concussion he suffered in testing.

Force India has been remarkably consistent in recent years, finishing sixth in the constructors' championship in three of the past four seasons. Matching that effort this season, though, will be a real challenge.

Traditionally, the team starts the season strongly before fading after the summer break, as its big-spending rivals out-develop it. But delays in the production of its 2015 chassis have put the team on the backfoot from the off.

One of the reasons is down to its decision to do all of its data gathering in Toyota's windtunnel rather than splitting between two different facilities.

The tunnel is considered one of the best in Europe, and although delays in getting use of it - caused by legal issues with the previous incumbent Caterham - have hampered development, Force India is convinced of the long-term benefits.

Sergio Perez and Nico Hulkenberg must wait until after Monaco for the first significant upgrade package, so up until then the team concedes it's about damage limitation.

We've seen very little from Nico Hulkenberg and Sergio Perez in winter testing, because of Force India's lack of running, but both drivers were extremely hopeful when talking about their hopes of the season.

Hulkenberg was impressive last season and got the job done in the two days he had behind the wheel of the VJM08 at the final Barcelona test.

The German is a pro at getting the most out of the car almost every time he gets behind the wheel. He scored in each of the first 10 races last year and 15 overall in a season of 19 races.

It's that kind of consistency that Hulkenberg will need to repeat if he wants to keep himself in the shop window for a drive further up the grid in the future.

If Hulkenberg can be relied upon to maximise the machinery, Perez's form is much more sporadic. The Mexican scored the team's only podium last year, in Bahrain, but threw away a good points haul when he collided with Felipe Massa's Williams in Canada. That said, he still managed 11 points-scoring finishes.

A stable line-up bodes well for the team and the drivers, but they will face a fight from the start to score points in a car that is way behind in terms of development.

Team principal Franz Tost has set ambitious targets. He says the STR10 is the best car ever produced from Toro Rosso's Faenza base, and reckons it must finish at least fifth in this year's constructors' championship.

That's a tall order for a team that placed seventh last season, 125 points adrift of sixth (Force India) and 151 points shy of fifth (McLaren).

To make up that shortfall, STR would have to multiply its 2014 scoring rate by at least a factor of six...

But there are genuine reasons to feel confident. McLaren and Force India are both on the back foot, while STR technical director James Key insists the team is now on top of the reliability problems that cost it heaps of extra points last year, which means its drivers should be in the hunt for regular top-10 finishes.

The question mark is whether a Mercedes-powered Lotus team will leapfrog ahead. If that happens, and McLaren-Honda gets its act together quickly, staying seventh in the standings may be the best STR can hope for.

Toro Rosso's top-five ambitions rest on two drivers with zero F1 starts between them, but that inexperience is counterbalanced by a abundance of youthful hunger, and two wise heads. Their rookie status is pretty much the only similarity between Max Verstappen and Carlos Sainz Jr, whose careers followed very different trajectories to this point.

Teenagers with only a year of car racing behind them don't get rocketed straight into F1 ahead of ostensibly better-qualified alternatives unless they're truly special.

Max Verstappen has plenty to learn but possesses an ideal combination of mature-beyond-his-years perceptiveness and swashbuckling raw talent.

His European Formula 3 fireworks demonstrated the latter, while the speed with which he has acclimatised to the F1 car showcased his mental aptitude. It's easy to see why Helmut Marko was in such a hurry to reach outside the Red Bull talent pool for him.

While Verstappen's career path has been vertically upwards, Carlos Sainz Jr has had to scrap his way into the Toro Rosso seat after being snubbed once in favour of Daniil Kvyat and then for Verstappen.

A Formula Renault 3.5 title and strong performance in a crunch F1 test for Red Bull earned him the seat and built a conviction that overcoming tough times had made him a stronger character and better driver than he would otherwise have been.

Testing included a couple of crashes, which Sainz put down to finding the limits of himself and the car at a less costly time than a grand prix weekend.

For an outfit that has such a rich racing heritage, both in terms of name and previous iterations of the team, Lotus let itself down last season with a car that was awful.

Three low points-scoring finishes were the highlights in a 2014 season that couldn't end fast enough.

Progress has been made over the winter, with Lotus rolling out a tighter, cleaner package that also has the benefit of Mercedes power for 2015.

Crucially, the team believes it understands the car better while Pastor Maldonado and Romain Grosjean say they have a better feeling when behind the wheel, which in turn makes it easier to drive.

All the signs suggest this will be a stronger year for Lotus.

Romain Grosjean's first full year in 2012 was, to all intents and purposes, an absolute shocker. The Frenchman showed flashes of speed but all too often found himself colliding with other drivers.

Six podiums the following year went a long way to putting that behind him and hopes of a good season and potentially a first win in 2014 were high - but the car was awful. Grosjean wasn't afraid to voice his frustrations, delivering some of the more entertaining team-radio soundbites. But he did his best with what he's had.

This year, the Frenchman's smile is back and following a successful test, he says he feels the car is a step forward and, importantly, easier to understand, which bodes well for development. If the E23 lives up to expectations, Grosjean should feature in the points regularly.

His team-mate Pastor Maldonado is aiming high this season, suggesting Lotus will be in a fight with Williams, Ferrari and Red Bull. That's certainly ambitious even if on his day Maldonado can be very, very fast - as the 2012 Spanish Grand Prix win attests.

Maldonado's problem is that his day doesn't roll around all that often. The Venezuelan's wheel-to-wheel combat leaves a lot to be desired, too, and his form is erratic, which together will ultimately hamper Lotus's hopes of climbing up the field.

When Marussia and Caterham hit financial woes at the end of last year, few expected either of them to make it back on the grid.

Caterham has indeed failed to find the funding it needed, but Marussia's former chiefs Graeme Lowdon and John Booth have worked their hearts out to resurrect their team.

The new Manor Marussia F1 outfit has found the backing it needs, secured its entry, overcome opposition from rivals as it made its 2014 car eligible for use as a stopgap, and is now focused flat-out on getting onto the grid in Melbourne.

But just making it out of the pits in Albert Park will only be the start of the journey that Manor needs to make. An updated 2014 car, with a year-old Ferrari engine, is going to face a hard time getting regularly within 107 per cent of pole position - something it will need to do to qualify.

That is why there will be an urgency for the team to gets its bespoke 2015 challenger ready as early as possible in the campaign.

It is not going to be an easy few months for the team - but in Lowdon and Booth, Manor has always had two men who will never give up without a fight.

Will Stevens is no stranger to being thrown in at the deep end, after making his Formula 1 debut for Caterham at last year's Abu Dhabi Grand Prix.

With Manor facing a race against time to just get a car ready for the start of the season, there is no expectation of an easy beginning to the year. In fact, just getting within 107 per cent of pole for qualifying will be success for now.

Stevens is a solid pair of hands though, and will be ready to knuckle down and go through the likely initial frustrations for the hope of seeing some progress further down the road.

Manor later confirmed former Caterham test driver Roberto Merhi would make his grand prix race debut in Australia.

Much like his new team-mate experienced last year, it will be in at the deep end for the Spaniard, who had been slated to race in Formula Renault 3.5 again after agreeing a deal with Pons.

Sauber hit rock bottom in 2014, after failing to score a single point and being forced to fight for survival amid Formula 1's escalating spending war.

That the Swiss team was able to keep things rolling on owed much to the efforts of team principal Monisha Kaltenborn, who refused to give up despite huge hurdles being placed in the way of F1's minnows.

And now, despite signing heavily backed drivers in Marcus Ericsson and Felipe Nasr, things remain tough. Promised cost-cutting measures have not come on board; engine bills are still very high and the commercial revenue is not enough to cover the money needed to go racing properly. The team is not out of the woods yet.

It is not all bad news at Hinwil though, for Sauber looks set to benefit from the progress that Ferrari has made with its engine over the winter. Last year's power unit was less powerful, less economical and heavier than the Mercedes - which left Sauber on the back foot.

The new power unit should not pose as many problems this year, and even on the car front there appear to have been solid gains. It may not be enough to get Sauber back in the fight for podium finishes, but it should be enough to end its points drought.

Delivering top-10 finishes will help Sauber get some belief back, as F1 faces a year where it must decide if it wants to support the small teams or not.

F1's financial crisis ended Marcus Ericsson's maiden season early as Caterham collapsed ahead of the United States Grand Prix.

But, with healthy backing behind him, it also helped him achieve a step up the grid as Sauber moved quickly to secure his services and grab the sponsorship benefits.

This season should give us a much better indication of Ericsson's overall potential, with last year's form a bit inconsistent. Although not helped by a weight disadvantage, there were too many mistakes and not enough strong days like Singapore.

If he can iron out the errors, and let his natural speed come through, he could produce some decent points-scoring results.

Rookie team-mate Felipe Nasr caused a bit of a shock when he landed the second Sauber seat for 2015 - as he effectively ended all race hopes for Adrian Sutil and Giedo van der Garde.

Some masterful play by manager Steve Robertson, plus some decent Brazilian backing, earned him a promotion from a Williams test role - and the Brazilian is eager to make the most of his opportunity.

His race wins and run to third overall in GP2 last year show he has talent on top of his backing, even if the overall championship eluded him.

A solid amount of testing mileage over the winter should allow him to feel comfortable enough to target the points that Sauber has not had since the end of 2013.